1. Field of the Invention
The invention relates to a method and apparatus for deciding a cause of abnormality in a plasma processing apparatus.
2. Description of the Related Art
In the steps in manufacturing a semiconductor, manufacturing apparatuses and inspection apparatuses of various types are used. For example, a plasma processing apparatus performs an etching process, a film forming process, and the like to an object to be processed such as a semiconductor wafer or a glass substrate by generating a plasma in a processing chamber. These processing apparatuses have a large number of parameters to control or monitor the operation states of the processing apparatuses. The processing apparatuses the operation states to make it possible to various processes under optimum conditions. As the parameters, temperatures of an upper electrode, a lower electrode, and the like arranged in a processing chamber.
When processes are performed by the above plasma processing apparatus, the plasma processing apparatus is controlled such that the processes can be always optimally performed while monitoring the parameters by detectors, respectively. At this time, the number of parameters comes to several tens. For this reason, when an abnormality is recognized in an operation state, a cause of abnormality is very difficult to be found out.
For example, in Japanese Patent Laid-open Publication No. 11-87323, the following technique is disclosed. That is, a plurality of process parameters of a semiconductor wafer processing system are analyzed to correlate the parameters to each other as analysis data, thereby detecting changes of process characteristics and system characteristics.
The following method is also known. That is, the plurality of parameters are held together into a smaller number of statistical data as analysis data by using a method of analyzing a principal component which is one of multivariate analyses. Operation states of a processing apparatus is monitored on the basis of the small number of statistical data to evaluate the operation states.
In such a conventional method, for example, analysis data is subjected to, e.g., a principal component analysis on the basis of the statistical analysis result obtained by the principal component analysis to calculate a residual score. The residual score is a predetermined value or more, it is decided that the analysis data is abnormal.
However, by the above methods, it can be decided whether the analysis data is abnormal or not. Of the parameters constituting the analysis data, a parameter which causes an abnormality cannot be specified.
With respect to this point, when degrees of contribution of the parameters in the analysis data are calculated to a residual score, a specific parameter which causes an abnormality can be known to some extent. More specifically, since a parameter having a high contribution largely contributes to a residual score of a part decided as an abnormal part, a parameter having a high contribution is abnormal with high probability.
However, a specific parameter cannot be decided as an abnormal parameter due to the contribution of a residual score. For this reason, a parameter which causes an abnormality cannot be appropriately specified.